This application is based on application No. 10-007319 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an image reading apparatus, and particularly to an image reading apparatus used for a digital copying machine and the like.
2. Description of the Background Art
According to one method of controlling the amount of light received by a photoelectric transducer section in a conventional image reading apparatus, the level of the amount of light illuminating an original document is preliminarily defined under the worst condition in system design. According to another method, the circuit gain is measured in advance by a substrate checker, and the measurement is fed back to the level of the amount of light illuminating the original document.
According to the method of preliminarily defining the level under the worst condition in system design and any conventional method of controlling the amount of light received by the photoelectric transducer section, there is scatter in gain and the like in each circuit, and a final A/D output value includes the scatter of each circuit. In the case of the method of preliminarily defining the A/D out under the worst condition in system design, the circuit never saturates on any condition. However, there is actually a considerable margin between the saturation level and the defined level because of the scatter in each circuit, resulting in unnecessary decrease in the quality of an image.
In the case of the method of measuring the circuit gain by the substrate checker, improvement relative to the scatter of the gain of each circuit is achieved. However, the scatter of the input/output saturation level of each device is not considered yet. In addition, although measurement of the circuit gain (and input/output saturation level in some cases) by the substrate checker or the like is effective, the cost of assembly would increase and the measurement would be required again when components are replaced.
An object of the present invention is to provide an image reading apparatus capable of taking full advantage of each device function and adjusting it even if each device function varies depending on respective machines.
According to one aspect of the present invention, an image reading apparatus is provided. The image reading apparatus includes an illumination unit directing light toward an original document, a transducer unit transducing the light directed toward the original document and reflected therefrom to an electric signal, and a controller controlling the amount of light from the illumination unit according to a saturation characteristic and a frequency characteristic of the transducer unit.
According to another aspect of the present invention, an image reading apparatus is provided. The image reading apparatus includes an illumination unit directing light toward an original document, a transducer unit transducing the light directed toward the original document and reflected therefrom to an electric signal, a change unit changing time for accumulating an amount of light at the transducer unit, and a controller controlling the time for accumulating an amount of light at the change unit according to a saturation characteristic and a frequency characteristic of the transducer unit.
Preferably, a detector detecting the saturation characteristic and the frequency characteristic of the transducer unit may be provided.
The detector can detect the saturation and frequency characteristics of the transducer unit by, for example, reading a pattern.
The pattern may have change in density in, as one example, a sub scanning direction.
The change in density in the sub scanning direction may be arranged to allow the density to gradually decrease.
The pattern may have change in density in, as another example, a main scanning direction.
Two degrees of the density may be alternately arranged, for example, to constitute the change in density in the main scanning direction.
According to the present invention, an actual machine can be manufactured taking full advantage of each device characteristic for combining respective devices. Consequently, enhancement in image quality is achieved.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.